1. Field of the Invention
The present invention relates to an image pickup apparatus such as a digital camera, and in particular to a structure of a lens barrel which the image pickup apparatus has.
2. Description of the Related Art
Digital cameras that are exemplary image pickup apparatuses storing images, which are obtained using an image pickup device such as a CCD or a CMOS, in a semiconductor memory or the like are becoming popular. In such digital cameras, the shooting angle of view is varied (so-called zooming operation) by changing the intervals between a plurality of lens groups.
In recent years, there has been an increasing demand for increasing zooming magnification while making a body (camera main body) thinner. Accordingly, a structure that enables miniaturization of a body while securing the longest possible movement strokes of lens groups is desired.
Therefore, in a so-called retractable zoom lens barrel, it is necessary to form cam grooves in cam cylinders in a manner extending in a direction of an optical axis so as to secure long movement strokes of lens groups. For example, there has been proposed an arrangement in which a cam groove is formed over the entire width of one extended cam cylinder in the direction of an optical axis so as to secure a long movement stroke of a lens group inside, and a cam groove is also provided outside the cam cylinder to hold a lens group and move the lens group in the direction of the optical axis (see Japanese Laid-Open Patent Publication (Kokai) No. 2010-156870). Also, there has been proposed an arrangement in which a cam groove is formed in a fixed cam cylinder, which is never extended, over the entire width thereof in a direction of an optical axis so as to secure a long movement stroke of a lens group inside (see Japanese Laid-Open Patent Publication (Kokai) No. 2001-228384).
However, according to the techniques described in Japanese Laid-Open Patent Publication (Kokai) No. 2010-156870 and Japanese Laid-Open Patent Publication (Kokai) No. 2001-228384, the number of optical systems such as lens groups that can be placed inside a cam cylinder is limited, and it is necessary to arrange the optical systems with consideration given to the balance between cam groove stroke and rotation phase. In this case, if the length of a cam cylinder in a direction of an optical axis is required to be long so as to form such a cam groove as to obtain a desired stroke, this will bring about upsizing of a lens barrel.